About Member Size Control

Thin trusses in the resulting structure are often undesirable, depending on the manufacturing process. Defining a minimum thickness avoids the creation of small substructures in the final result.

The minimum member size control technique ensures the mesh independence of the results. A coarse mesh and a fine mesh lead to the same optimized topology if the minimum member sizes for both cases are set to the same absolute size.

Note: In both cases the size should be larger than the average element edge length.

Optimized engine support with and without MINIMUM member size restriction is presented in the following figure:

Note:

• It is not possible to ensure the accurate minimum thickness of the structures. For some cases, the results contain parts with a diameter smaller than the defined minimum member size.
• The CPU-time for the calculation increases quadratically with the minimum member size. To save calculation time, the restriction should only be defined in the areas of the model where thin parts should be avoided. To identify these areas, the first step is to perform an optimization without restrictions.

The definition of a maximum truss thickness is often necessary in order to design the components produced by casting. With this restriction, thick parts are avoided by splitting them into several thinner parts.

Normally, the maximum member size control is also a minimum member size control. In the restriction area, the resulting structure contains trusses mainly of the given defined diameter. Generally, no thinner trusses exist. Usually, the combination of a maximum member size control and a minimum member size control is not required.

The following figure shows a plate designed with and without maximum member size control: